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1. Field of the Invention
The invention is related to the field of fiber optic communication systems, and in particular, to fiber optic systems that provide errorless switching.
2. Description of the Prior Art
FIG. 1 depicts the current system of switching used in fiber optic networks. A first node 101 connects to a second node 102 via a first optical fiber 150 and a second optical fiber 160. The second node 102 is comprised of a first optical-to-electrical converter 120, a second optical-to-electrical converter 121, a first fault detector 130, a second fault detector 131, and a switching system 140. The first optical-to-electrical converter 120 connects to the first node 101 via the first optical fiber 150. The first optical-to-electrical converter 120 connects to the first fault detector 130 via electrical data line 151. The first fault detector 130 connects to the switching system 140 via electrical data line 153 and electrical control line 152.
The second optical-to-electrical converter 121 connects to the first node 101 via the second optical fiber 160. The second optical-to-electrical converter 121 connects to the second fault detector 131 via electrical data line 161. The second fault detector 131 connects to the switching system 140 via electrical data line 163 and electrical control line 162.
In operation, the first node 101 transmits a first data signal over the first optical fiber 150. The first optical-to-electrical converter 120 receives the first data signal and converts it from an optical signal to an electrical signal. The first optical-to-electrical converter 120 transfers the first data signal to the first fault detector 130 via electrical data line 151. The first fault detector 130 determines if an error has occurred in the transmission of the first data signal and generates a first error instruction if an error has occurred. The first fault detector 130 transfers the first data signal to the switching system 140 via electrical data line 153. The first fault detector 130 transfers any first error instructions to the switching system 140 via electrical control line 152.
The first node 101 transmits a second data signal over the second optical fiber 160. The second optical-to-electrical converter 121 receives the second data signal and converts it from an optical signal to an electrical signal. The second optical-to-electrical converter 121 transfers the second data signal to the second fault detector 131 via electrical data line 161. The second fault detector 131 determines if an error has occurred in the transmission of the second data signal and generates a second error instruction if an error has occurred. The second fault detector 131 transfers the second data signal to the switching system 140 via electrical data line 163. The second fault detector 131 transfers any second error instructions to the switching system 140 via electrical control line 162.
The switching system 140 receives the first data signal, the second data signal, and any first or second error instructions. The switching system 140 transfers either the first data signal or the second data signal. The signal that gets transferred depends on the first error instruction and the second error instruction. For example, if an error occurs on the first data signal, the first error instruction instructs the switching system 140 to transfer the second data signal and not the first data signal. If an error occurs on the second data signal, the second error instruction instructs the switching system 140 to transfer the first data signal and not the second data signal.
Two problems exist with the system in FIG. 1. One problem is that duplicate data can be transferred in the switching process. For example, consider the situation where the second data signal lags behind the first data signal. The lag in the second data signal causes the signals to be mis-aligned at the switching system 140. Assume for this example that the second data signal lags the first data signal by ten blocks of data. When the switching system 140 changes from transferring the first data signal to transferring the second data signal, those ten blocks of data have already been transferred on the first data signal. After the switching system 140, the ten blocks of data will again be transferred on the second data signal. The amount of duplicated data depends on how far the second data signal lagged behind the first data signal.
Another problem is that data can be lost in the switching process. Consider the other situation where the first data signal lags behind the second data signal. The lag in the first data signal causes the data to be mis-aligned at the switching system 140. Assume for this example that the first data signal lags the second data signal by ten blocks of data. When the switching system 140 changes from transferring the first data signal to transferring the second data signal, ten blocks of data will have been missed. The amount of data lost depends on how far the first data signal lags behind the second data signal.
Errorless switching exists in other communications networks such as microwave communication networks, but doesn""t exist in fiber optic systems. Fiber optic communication networks traditionally utilize Synchronous Optical Network (SONET) rings to provide two transmission paths to switch between. These fiber optic communication networks do not provide for errorless switching. By today""s standards, switching resulting in duplicate or lost data is not acceptable.
The invention solves the above problem by aligning the first data signal with the second data signal in the optic node before switching occurs. Data is not lost or duplicated in the switching process.
The errorless switching system is comprised of a first fault detector, a second fault detector, a synchronization system, and a switching system. The synchronization system aligns the first data signal with the second data signal. The fault detectors detect errors in the data signals and instruct the switching system to transfer the first data signal or the second data signal to avoid transferring erroneous data. No data is lost or duplicated because the data signals are aligned at the switching system.